Spark plug tester



H. RABEZZANA` May 8, 1934.

SPARK PLUG TESTER Filed Aug. 21. 1,953

Patented May 8, 1934 SPARK PLUG TESTER Hector Rabezzana, Flint, Mich., assigner to A Spark Plug Company, Flint, Mich., a company D of Michigan Application August 2l, 1933, Serial No. 686,045

11 Claims.

This invention relates to an improved device for testing the operating condition .of an' engine spark plug without removing the plug from the engine.

5 Maximum spark plug. efficiency is dependent to a large extent upon the size of the 'gap and the amount of current that by-passes the gap. An accumulation of carbon on the insulator between the electrodes providesv a shunt around l@ the gap, and is responsible for current losses and consequent weakening of spark intensity. Prod- 'ucts of combustion begin to deposit on the plug parts exposed in the engine combustion chamber. 'as soon as the plug is put into use, and continue it; with each explosion to build up andoffer less resistance in the shunt circuit afforded thereby. As time goes on current leakage increases through the fouling conductance, and finally a point is .reached where only a slight additional deposit a@ will seriously impair sparking action.

With this in. mind, it is proposed to provide va testing device embodying a 4spark actuated indicatonand a shunt, having a conductance of v a valuesuch that leakage through the shunt 215 will noticeably affect sparking only in the event fouling conductance has so increased that a slight additional deposit will reduce its resistance to the -point where the gap is practically shorted completely.

ao With the use of the tester, the spark actuated indicator, preferably in the form of a neon tube, .will flash with each jump of current across the gap, the brilliancy of the ilash showing the intensity of the spark. However, if current losses,

through fouling conductance, are considerable, then the added diversion of current through the resistance in the tester shunt circuit will so reduce the voltage that the plug will fail' to re properly and the dimness or lack of flasher light 4o indicates the condition to an observer. Any plug giving a poor actionron test should be removed,

cleaned, and regapped, and then retested; Unless a fairly bright ash results, the plug should be discarded for the indication is that the life of the plug insulator has practically ended, and

its effectiveness destroyed by foreign matter permanently embedded in its surface, and which ordinary methods of cleaning do not eliminate.

An object of the present invention is to incor- 5o porate the spark actuated indicator and shunt resistor in a compact assembly within a small and convenient pencil-like housing, which a me- .chanic can readilyhold in one hand lduring a test, and carry on his person-when not in use,

55 such pencil being devoid of projecting wires orV other awkward attachment devices, but having instead, xed terminals for the resistor shunt circuit', which'may be easily brought to contact with the spark plug parts.

Preferred embodiments of the compactly assembled instrument are illustrated on the accompanying drawing, wherein Figures 1, 2 and 3 each show in longitudinal section, alternative constructions positioned in testing relation to spark plugs, and Figure ais a detail view with parts broken away and looking in theV 'direction of the arrows on line 4-4, Figure l.

Referring to the drawing, the spark plug shown comprises an insulator core 1, separating inner and outer metallic members2 and 3, with which are respectively associated sparking electrodes 4 and 5. For simplicity of illustration, `the spark plug is shown removed from an engine cylinder, but it is pointed out that actualtesting would take place with the plug positioned in the engine and connected inits normal fashion in the engine ignition circuit, so that the test would be under ordinary compression and ignition conditions.

The instrument shown in Figure l includes a neon tube 6 and a self-supporting resistor element 7, arranged in longitudinally alined succession Within arr axial bore of the pencil hous-` ing 8, which is preferably formed of insulating material, such as transparent bakelite. One end of the bore may be closed by a metal cap or terminal 9, fitting exteriorly of the tubular housing 8 and having'its skirt portion inwardly deformed behind an annular rim l0 at the end of the tube to hold the parts in place. With this terminal 9 contactsv one end of the resistor element 7. The resistor may comprise a molded carbon or graphite rod, having a preselected resistance, and each` end is preferably sprayed as at 11 with brass to insure a good electrical contact between cooperating end seats.

The'selected resistance of the element 7 will be determined by the particular type of spark plug for a given engine on which the mechanic specializes his Work. For example, a resistance of 300,000 ohms would be suitable for testing one type of plug, while a resistance of 600,000 ohms would be necessary for testing another type of plug, and still other resistances would be provided to meet various conditions.

The value of a given resistance may be printed for convenience on an opaque Wrapping 12, such as paper, andthe notice would be visible through the transparent wall of the pencil 8. Incidentally, this paper wrapping 12 about the resistance could also carry the manufacturers trade mark or other printed advertising or decoration. The primary purpose of the paper, however, is to conceal the resistor and improve the general appearance of the instrument.

Located intermediate the opposite ends of the bore to provide a seat for the innermost end of the resistor 7, is a division wall or metal plug 13 having a radial or lateral opening, in which is slidably received a. shoe or plunger 15 and a pressure exerting spring 16. This spring pressed plunger extends through an opening 17 in the wall of the tubular insulator 8 and seats within an annular groove formed in an exterior metal sleeve 18, thus providing an interlock between the parts and an electrical connection with the resistor 7 and sleeve 18, the sleeve aording a contact or terminal.

Interposed between the wall 13 and an adjacent end of the neon tube 6 is a coil spring 19, which electrically connects the neon tube with the wall 13 and tends to resiliently urge the parts away from each other and maintain good electrical contact between the opposite ends of the resistor 7 and metallic seating portions therefor. The spring also compensates for expansion of the parts and eliminates the need for extreme -accuracy in manufacture. The far end of the tube 6 may be seated on resilient or soft packing material 20, which together with the coil spring 19 y and into the bore of the division wall 13 and the sleeve 18 is slid over the parts to seat the spring pressed plunger in the pocket of the sleeve.

For testing a plug, the device, held in one hand, is brought to the plug and the terminal 9 rested against either the outer metallic part 3 or with some grounded portion of the engine, while the terminal sleeve 18l is rested against the inner metallic plug member 2 or the cable connector thereon. This will provide a shunt circuit between'\the terminals 9 and 18 and through the resistor 7 to affect the action of the current flow across the terminals 4 and 5, as before pointed out. With each discharge of current across the spark gap, the neon tube will be lighted momentarily and the ash observed through the window 22.

In the embodiment shown in Figure 2, the pencil body 25 terminates in a reduced tip portion 26, in which is embedded a metal terminal 27. The opposite end of the pencil 25 is internally screw threaded to receive a removable plug 28. The neon tube 29 and the resistor 30 are successively inserted within the bore of the metal tube, with their adjacent ends spaced apart by the coil spring 36 and their remote ends seated on the plug 28 and metal electrode 27, respectively. A conductor strip 31 has an angular leg 32 inserted under the coil spring -36 and against the end of the resistor 30, while its opposite end is formed into an arcuate shoe 33 that projects through an opening in the wall of the pencil into engagement with a sleeve 34. A reversely bent finger 35 integral with the sleeve 34 extends beside the pencil body in generally ogee configuration, to a point considerably below the terminal 27 and constitutes a grounding terminal for the resistance element. This clip also aiords a safety catch to hold the instrument in the pocket of a mechanics clothing.

The axial bore of the pencil 40 in Figure 3, is closed by the screw threaded terminal 4l, against which is seated one end of the' resistor 42. The other end of the resistor contacts with the expansion spring 43, which also seats the neon tube 44. In this case the sleeve 45 is held in place by a set screw 46, in contact with one end of the resistor 42 for grounding the shunt circuit through the sleeve 45 and its associated pocket clip, which for convenience, may comprise hinged sections 47 and 48. The extended position of the sections 47 and 48 is illustrated in the full lines, while the folded position of the end section 48is illustrated by the broken lines, it being understood that the clip is folded to make the instrument more compact when not in use.

I claim:

1. A spark plug testing device comprising a pencil-like body of insulating material having an axial bore, a flasher unit and a resistance unit arranged in longitudinal succession within the bore, said resistance unit being in the form of a body of high resistance material, a pair of spaced terminals electrically provided by said resistance unit and adapted for connection respectively on opposite sides of the spark gap in a spark plug circuit to shunt current through said body, and means electrically connecting said ilasher unit to the shunt.

2. Means for testing an engine spark plug while the engine is running under its own compression -and ignition conditions, including a lumped resistance unit in the form of a body of high resistance material adapted for connection with the spark plug circuit in shunt relation to the spark gap, a spark actuated indicator unit, associated with the shunt for actuation incident to current iiow through the body, and a pencillike insulator body having an axial bore enclosing said units in longitudinally alined succession.

3. In a spark plug testing device, a pencil-like body of transparent material having an axial bore, a spark actuated5 indicator and a shunt cir- 4. In a spark plug testing device, a pencil-like body having an axial bore, a spark actuated indicator and a shunt circuitresistor in the form of a body of high resistance material positioned longitudinally within the bore in succession, a terminal mounted at one end of the body and adapted to seat one end of the resistor, a terminal mounted intermediate the ends of the body and a contact connection between the last mentioned terminal and the opposite end of the resistor whereby the resistor provides a closed path for'current flow between said terminals.

5. In a spark plug testing device, a tubular housing, a spark actuated indicator and a shunt resistance element in the form of a body of high resistance material enclosed within the housing in longitudinal succession, a spring interposed between adjacent ends of the indicator and resistance element, and seats in the housing for the remote ends ofthe indicator and resistance element.

6. For testing spark plugs having inner and outer metal members associated with the sparking terminals and separated by an insulator, a

hand tool comprising a tubular body of insulating material, an intermediately positioned division wall dividing the interior of the body into two chambers, a spark actuated indicator in one of said chambers, a coil spring under compression between the wall and indicator, a shunt resistor Within the other chamber bearing at one end on the wall, a terminal bearingv for the other end of the resistor carried by the housing for contact with a metal member of a spark plug and a terminal connected with the division wall through the housing wall for contact with the other metal member of the plug.

'7. A spark plug tester including a tubular housing, a terminal at one end of the housing, a resistor enclosed by the housing and seated on said terminal, a closure device for the opposite end of the housing, a spark actuated indicator within the housing seating on said closure device, a coil spring interposed between adjacent ends of the indicator and resistor, a conductor having one end held between the spring and resistor with its opposite end extending through an opening in the housing and a terminal element carried by a sleeve closing said opening and engaging the conductor.

8. vA spark plug vtester including a pencil enclosing a spark actuated indicator and a resistor element, a resistor terminal mounted at the end of the pencil, a set screw passing through the pencil wall and engaging the resistor at the end opposite said terminal, a 4s leeve held on the pencil by said'screw, and a pocket clip associated with the sleeve and provided at its end with a.

hinged n er lwhich may be extended beyond the first mentioned terminal.

9. In a spark plug tester device, a housing, a pair of space contact elements carried by the housing and a apted shunt relation ith a spark plug ignition circuit, means electric connecting said contact elements and compr ing a self supporting body of porous material having electrical resistance of selected value with i s Contact engaging portions coated with material of relatively low resistance, and a spark actuated indicator enclosed within the housing for association with the shunt.

10. In a spark plug te ter, a housing, spaced contact elements carried b the housing for connection in shunt with the spark plug ignition circuit, a stick of resistance material electrically bridging the space between said elements and -having integral with its opposite end portions a brass coating to insure good electrical connection with said elements, and a spark actuated indicator device enclosed by the housing.

` 11. A spark plug tester, comprising a pencillike body of insulating material having an axial bore, a pair of spaced terminals carried by the housing for shunt connection with the spari; plug ignition circuit, a spark actuated indicator and a conductor arranged in longitudinal succession within the bore of the housing with said conductor bridging the space between said terminals'and having a resistance of given value to current flow through the spark plug shunt.

HECTOR RABEZZANA.

for electrical connection in 

